Scientists Measure Mass, Density of Eros

Planetary scientists have made their best
measurement yet of the mass and density of
the near-Earth asteroid Eros and have
concluded it is not a rubble pile, unlike
other asteroids.

In a pair of papers published in the July
23 issue of the journal Science, members of
two science teams associated with the Near
Earth Asteroid Rendezvous (NEAR) mission
reported on the size, mass, and density of
the asteroid 433 Eros, the second-largest
of all know near-Earth asteroids.

NEAR SPACECRAFT REVEALS MAJOR FEATURES OF EROS

Asteroid 433 Eros is slightly smaller than predicted, with at
least two medium-sized craters, a long surface ridge and a density
comparable to the Earth's crust, according to measurements from
NASA's Near Earth Asteroid Rendezvous (NEAR) spacecraft.

NEAR's science instruments observed about two-thirds of Eros
on Dec. 23, 1998, as the spacecraft flew by the asteroid following
an unsuccessful firing of its main engine a few days earlier. A
subsequent successful firing of the engine put NEAR on course to
rendezvous with Eros to begin its planned yearlong orbital mission
starting in mid-February 2000.

Scientists and engineers at The Johns Hopkins University
Applied Physics Laboratory (APL) in Laurel, MD, which manages the
mission, and science team members from affiliated institutions
quickly planned the valuable flyby observations in the wake of the
unsuccessful engine burn on Dec. 20.

During the flyby, 222 photos and supporting spectral
observations of Eros were taken from as close as 2,375 miles
(3,830 kilometers) from the asteroid by the spacecraft's
multispectral imager, infrared spectrometer and radio science
experiment. "The flyby of Eros has given us fundamental
information that will help us plan a better orbital mission at
Eros," said Dr. Andrew F. Cheng, NEAR project scientist at APL.
"It has taken some of the risk out of our orbit insertion maneuver
and early operations."

First observed from the Earth more than 100 years ago, Eros
was known to be an S-type asteroid with high concentrations of
silicate minerals and metal. However, few details about its
structure or composition are observable from the ground. The NEAR
flyby produced evidence of variations in surface color and
reflected light (or albedo) that suggest the asteroid has a
diverse surface makeup. Closer observations during the
comprehensive yearlong orbital study of Eros will be needed to
determine its precise composition.

The science team has determined that Eros is slightly smaller
than originally estimated from ground-based radar observations,
with a size of 21 by 8 by 8 miles (33 by 13 by 13 kilometers),
versus an estimate of 25.3 by 9 by 8 miles (40.5 by 14.5 by 14
km). The asteroid rotates once every 5.27 hours and has no
discernible moons.

The asteroid's density is approximately 1.55 ounces per cubic
inch (2.7 grams per cubic centimeter), close to the average
density of Earth's crust. This makes Eros about twice as dense as
asteroid 253 Mathilde, a C-type, carbon-rich asteroid that NEAR
flew past in June 1997, and about the same density as S-type
asteroid 243 Ida, which NASA's Galileo spacecraft flew past in
1993. Eros and Ida are the only S-type asteroids for which mass
and density have been determined.

Flyby imaging of the asteroid's surface revealed a prominent
elongated ridge that extends along its length for as much as 12
miles (20 km). "This ridge-like feature, combined with the
measurements of high density, suggests that Eros is a homogeneous
body rather than a collection of rubble" such as Mathilde appears
to be, said Dr. Joseph Veverka, of Cornell University, Ithaca, NY,
who heads the mission's imaging team. "It might even be a remnant
of a larger body that was shattered by an impact."

The surface of Eros is pocked with craters. The two largest
craters are four miles and 5.3 miles (8.5 and 6.5 km) in diameter,
less than half the size of asteroid Mathilde's largest craters.
The existence of fewer, smaller craters could be an indication
that Eros has a relatively young surface when compared to Ida.

NEAR and Eros will cross paths again in February 2000. The
spacecraft will then be inserted into orbit around the asteroid
and begin its yearlong study. Images taken during orbit are
expected to have more than 200 times better resolution than those
obtained during the flyby and will be taken from as close as nine
miles (15 km) from the asteroid's surface.

Flyby images of Eros and a related movie, an asteroid shape
model and a chart of spectral observations are available on the
NEAR mission Web site.

Two Views of Eros

This pair of images of the asteroid Eros was acquired by
the Near Earth Asteroid Rendezvous (NEAR) spacecraft on
December 23, 1998, as the spacecraft flew by the night
side of the asteroid at a distance of 2300 miles (3800
kilometers) at 1:43 PM EST. These views, taken at 1:44
PM and 2:05 PM EST as the spacecraft range increased
from 2300 miles to 2500 miles (4100 kilometers), show
only a tiny portion of the day side of Eros (phase angle
~119°). The smallest resolved detail is approximately
1300 feet (400 meters) across.

A firing of the main engine at 5 PM EST December 20,
designed to slow the spacecraft for insertion into orbit
around the asteroid, was aborted by the spacecraft.
Contact with ground controllers was temporarily lost,
but was regained at 8 PM EST December 21 when autonomous
spacecraft safety protocols took over and transmitted a
signal to the ground. All spacecraft systems were
determined to be healthy and operational. Within hours,
a flyby observation sequence was developed and uploaded
to the spacecraft. 1026 images were acquired by the
multispectral imager, to determine the size, shape,
morphology, rotational state, and color properties of
Eros, and to search for small moons. The infrared
spectrometer measured spectral properties of the
asteroid to determine what minerals are present, and the
magnetometer searched for a natural magnetic field.
Analysis of the spacecraft radio signal will yield
bounds on the asteroid's mass and density.

The main engine was fired successfully on January 3,
1999, placing NEAR on-course for a February 2000
rendezvous. Eros is NEAR's second asteroid encountered.
On June 27, 1997, NEAR flew by the main-belt asteroid
Mathilde at a range of 1212 kilometers (750 miles).

Built and managed by The Johns Hopkins University
Applied Physics Laboratory, Laurel, Maryland, NEAR was
the first spacecraft launched in NASA's Discovery
Program of low-cost, small-scale planetary missions. See
the NEAR web page at http://near.jhuapl.edu for more
details.

At noon, EST, January 3, the NEAR mission team conducted
a 24-minute, large bipropellant engine burn, to increase
the spacecraft's speed for a rendezvous with Eros in
February 2000. Preliminary indications are that the burn
was successful. NASA's Deep Space Network, which is
tracking the NEAR spacecraft, is expected to confirm the
accuracy of the burn early Monday morning, January 4.

The burn increased NEAR's speed by 2,100 mph (940 meters
per second) to catch up to the faster-moving Eros
asteroid, which overtook NEAR during the Dec. 23rd
flyby. At the time of the burn, the spacecraft was
565,650 miles (910,100 kilometers) from Eros

Once accuracy figures from the burn are received, plans
will be finalized for a small hydrazine engine burn to
correct any deviation from the spacecraft's intended
location. This burn is expected to take place in one to
two weeks. Periodic trajectory correction maneuvers will
be executed by the Mission Operations Center as deemed
necessary to keep the spacecraft on course during its
yearlong journey to the asteroid.

For now, NEAR continues on its orbit around the sun,
traveling at about 43,000 mph (19 kilometers per second)
as it gains on asteroid Eros.

December 24, 1998

Because of the failure of an engine burn needed to begin orbital insertion,
the NEAR spacecraft's orbit of asteroid Eros has been postponed for more
than a year, from January 1999 to May 2000.

David Morrison

The NEAR Spacecraft to Fly by Asteroid Eros on Dec. 23; Rendezvous with Eros in 2000

A Dec. 20 spacecraft abort of the initial rendezvous burn of the Near Earth
Asteroid Rendezvous (NEAR) spacecraft has resulted in a postponement of
NEAR's orbit of asteroid 433 Eros, originally scheduled for Jan. 10, 1999.
However, a flyby of the asteroid is planned for Dec. 23, 1998, at 1:43 p.m.
EST, that will provide valuable information for its later study.

"While the engine burn abort was unfortunate, we still expect to accomplish
the rendezvous objectives, but at a later date," says NEAR Mission Manager,
Dr. Robert W. Farquhar, of The Johns Hopkins University Applied Physics
Laboratory, which manages the NASA mission. "We expect that the later
rendezvous date will not diminish the overall science return."

During the Dec. 23, 1998, flyby, scientists will gain a preview look at the
asteroid and gain a global perspective that will provide important
information in planning an orbit insertion. Mission designers are now
expecting the rendezvous will take place by May 2000. Data obtained from
the flyby will help determine the shape and size of the asteroid and if it
has any moons.

The rescheduling of the NEAR mission was made necessary by the abort of a
planned 20-minute engine burn on Dec. 20, 1998. The spacecraft aborted just
seconds after initiation of the bipropellant burn, causing communications
with the spacecraft to be lost for about 27 hours. Contact was
reestablished early Dec. 22, after NASA's Deep Space Network locked onto a
radio signal from the NEAR spacecraft at about 8 p.m. EST, on Dec.21.

Responding to a command from the Mission Operations Center, NEAR started
downloading stored data early Dec. 22, which the mission team has been
analyzing to determine the cause of the abort and why the spacecraft lost
attitude control. "We've looked at the data and we believe there has been
no damage to the spacecraft or the propulsion system," says spacecraft
systems engineer, Andrew G. Santo. "Our fault protection software
identified the problem and switched NEAR to a safe mode. Essentially, it
worked as designed."

During the Dec. 23 flyby NEAR will take over 1100 images from as close as
4,100 kilometers (2,500 miles). Although the images will be of lower
resolution than those taken June 27, 1997, during the flyby of asteroid 253
Mathilde, they will provide scientists with important information about the
asteroid.

NEAR will then travel in an orbit around the sun that nearly matches that
of Eros. In May 2000, the spacecraft and Eros will meet, making it possible
to insert NEAR into orbit around the asteroid.

NEAR Spacecraft Makes Planned Flyby of Asteroid Eros

On Dec. 23, at 1:43 p.m. EST, the NEAR spacecraft made a
flyby of Eros designed to provide scientists with
detailed data on the asteroid. In a matter of hours,
mission operations personnel were able to respond to an
aborted scheduled engine burn and program the command
sequence that put the spacecraft on a trajectory
approximately 2,500 miles (4,100 kilometers) from the
surface of the asteroid. Currently (Dec. 23, 3 p.m.
EST), the spacecraft is executing the command sequence
as planned.

Three instruments onboard the spacecraft, the
Multispectral Imager, the Near-Infrared Spectrometer,
and the Magnetometer, are operating as expected. More
than 1,100 images of the asteroid are anticipated, which
will provide scientists with valuable information on the
size, shape, and surface characteristics of Eros and
whether it has any moons.

The first photographs will be posted on the NEAR Web
site on Dec. 24 between 1:00 - 2:30 p.m.

NEAR Sends Back Images of Eros

(December 24, 1998, 2 p.m. EST)

Despite an aborted engine burn that postponed the
January 1999, rendezvous of the NEAR spacecraft with
asteroid Eros, mission operations team members were able
to quickly upload new commands to the spacecraft, making
it possible to obtain valuable information during a
December 23, flyby of the asteroid.

Science data, including multicolor images, spectral
data, and magnetic field measurements taken during the
flyby, are now coming into the Applied Physics
Laboratory's NEAR Science Data Center. Doppler
navigation data and real-time telemetry were collected
that will help determine the mass of the asteroid.

The flyby gave NEAR Mission Operations an opportunity to
test tracking and instrument sequences in preparation of
a rendezvous event, says Mission Operations Center
Manager Mark Holdridge. "The flight recorders, full of
Eros science data, are being played back at the present
time. The spacecraft is healthy and doing just fine and
it has been confirmed that the flyby pointing and
instrument command sequence executed flawlessly to
completion."

In addition to flyby data processing, team members are
also studying data sent by the spacecraft soon after
contact with it was reestablished on Dec. 22, following
27 hours of communication blackout to determine the
exact nature of the software anomaly that led to the
rendezvous burn failure.

NEAR and Eros are now traveling in separate orbits
around the sun as plans are being made for a rendezvous
sometime between August 1999 and April 2000.

Images of Eros taken during the flyby are being posted
on the NEAR Web site as they are processed.

This montage of the asteroid Eros was assembled from
images acquired by the Near Earth Asteroid Rendezvous
(NEAR) spacecraft on Dec. 23, as the spacecraft flew by
the asteroid at a distance of 2,500 miles (4,100
kilometers) at 1:43 p.m. EST. This montage shows the
first nine of 28 views of Eros that were obtained during
the flyby. The images were taken between 10:44 AM and
12:44 PM EST as the spacecraft range closed from 7300
miles (11,100) km to 3300 miles (5300 kilometers).
During that time, the asteroid completed nearly half of
a rotation. The smallest resolved detail is
approximately 1650 feet (500 meters) across.

A firing of the main engine at 5 PM EST December 20,
designed to slow the spacecraft for insertion into orbit
around the asteroid, was aborted by the spacecraft.
Contact with ground controllers was temporarily lost,
but was regained at 8 PM EST December 21 when autonomous
spacecraft safety protocols took over and transmitted a
signal to the ground. All spacecraft systems appear
healthy and operational. Within hours, a flyby
observation sequence was developed and uploaded to the
spacecraft. Over 1100 images were acquired by the
multispectral imager, to determine the size, shape,
morphology, rotational state, and color properties of
Eros, and to search for small moons. The infrared
spectrometer measured spectral properties of the
asteroid to determine what minerals are present, and the
magnetometer searched for a natural magnetic field.
Analysis of the spacecraft radio signal will yield
bounds on the asteroid's mass and density.

Options for rescheduling firing of the main spacecraft
engine are currently being examined, and could lead to
Eros rendezvous and orbit insertion as early as mid-1999
or as late as May 2000. Eros is NEAR's second asteroid
encountered. On June 27, 1997, NEAR flew by the
main-belt asteroid Mathilde at a range of 1212
kilometers (750 miles).

Built and managed by The Johns Hopkins University
Applied Physics Laboratory, Laurel, Maryland, NEAR was
the first spacecraft launched in NASA's Discovery
Program of low-cost, small-scale planetary missions. See
the NEAR web page at http://near.jhuapl.edu for more
details.

December 21, 1998

NEAR RENDEZVOUS BURN ABORTED

The NEAR mission team is trying to reestablish communications with the spacecraft. Communications ceased during the first of four rendezvous burns that
would put the spacecraft at optimum speed and location for a Jan. 10, 1999,
rendezvous with asteroid 433 Eros.

Doppler data leads team members to believe that the spacecraft was transmitting at that time. Around-the-clock strategy sessions are being held to correct the problem. If communications are not established soon it is highly unlikely that the spacecraft will go into orbit on January 10.

December 21, 1998

NEAR Rendezvous Burn Aborted

The first rendezvous burn of the NEAR spacecraft's
bipropellant engine, scheduled for Dec. 20, at 5 p.m.
EST, was not completed as planned. Except for brief
communication shortly after the scheduled 20-minute burn
period, contact with the spacecraft has been lost.
Mission Operations is now working to reestablish contact
based on expectations that NEAR has entered safe mode
after the burn was aborted by the spacecraft.

Space probe on track for asteroid encounter

Officials said Wednesday the Near-Earth Asteroid Rendezvous (NEAR)
spacecraft will begin a series of rocket firings on January 10 that will aim
the small craft directly at the asteroid known as 433 Eros.

The craft is to dip within nine miles of Eros' surface during about a year
of orbital operations.

NEAR launched in February 1996 as a joint project between NASA and the Johns
Hopkins University Applied Physics Lab, and it is the first space mission
aimed at orbiting and probing an asteroid.

Instruments aboard the spacecraft will determine the composition and mass of
the 24-mile (38-km) long shoe-shaped object.

After the initial science objectives are completed, mission controllers plan
to become more adventurous, orbiting ever closer and perhaps even landing on
the asteroid's dusty surface, said mission manager Robert W. Farquhar.

"By taking the risk, we're hoping to get a lot of bonus science," Farquhar
said.

Officials hope the mission will provide answers to fundamental questions
about the nature and origin of near-Earth objects, such as the numerous
asteroids, meteoroids, and comets in the vicinity of Earth's orbit.

Officials said they are interested in learning the composition and density
of asteroids as part of fundamental research that would be needed to defend
the Earth against any potential collision with a space rock of destructive
size.

Farquhar said it would be important to know how to operate on and near such
a small body in the event that an asteroid aimed at Earth is ever found. One
scenario for protecting the Earth from such a collision is to land nuclear
weapons on its surface and shatter the object.

In order to do this, officials said, they have to understand the composition
and strength of typical asteroids.

Scientists believe an asteroid collision with Earth was likely responsible
for the mass extinction at the end of the Cretaceous period, and another
impact in 1908 destroyed thousands of square kilometers of forest near
Tunguska, Siberia.

Asteroids are thought to be the building blocks of the solar system --
aggregates of rock and dust that were left over after the formation of the
planets. Most of the asteroids are in the so-called astrobelt between the
orbits of Mars and Jupiter. Eros, however, is on an orbit that swings it
past Mars and close to the orbit of Earth.

Eros poses no threat. Its last pass went by the planet in 1975, missing by
45 million miles.

In June 1997, the NEAR spacecraft passed within 750 miles of an asteroid
known as Mathilde and sent back photos of features as small as a football
field. The photos of Eros should be far more detailed, scientists said.

The NEAR mission is the first launch in the Discovery Program, a NASA
initiative for small planetary missions with a maximum three-year
development cycle and a cost capped at $150 million for construction,
launch, and 30 days of operation.

Space Science News

December 16th

NASA's NEAR spacecraft may find that asteroids need dusting -
NASA scientists think that asteroids scoop up dust from space over the eons,
possibly blanketing themselves in layers up to a meter thick. Asteroids are
too small for gravity to capture dust, but static electricity might do the job
instead. If this idea is correct, then asteroids could provide storehouses of
primordial matter from the early Solar System for future exploration.

UA SCIENTIST ON 'NEAR' MISSION AMONG THOSE TO GET THE FIRST LONG,
CLOSE-UP LOOK AT AN ASTEROID IN SPACE HISTORY

On Sunday, Dec. 20, the NEAR (Near Earth Asteroid Rendezvous) spacecraft
will initiate a series of rocket engine firings that accelerate it
toward a rendezvous with a faster-moving asteroid, 433 Eros. NEAR will
reach Eros next month to begin the first close-up and comprehensive
study of an asteroid in space history.

"This is the first time ever a spacecraft will orbit an asteroid," said
Professor William V. Boynton of the Lunar and Planetary Laboratory at
The University of Arizona in Tucson. "There have been flybys and
snapshots, but not much in the way of quantitative scientific data."

Boynton is on one of six science teams that will study 433 Eros on the
year-long NEAR mission that begins on Jan. 10 and is scheduled to end
Feb. 6, 2000. The asteroid, which measures 24 miles in length and 10
miles in diameter (40 kilometers x 17 kilometers) was the first
near-Earth asteroid (those whose orbits come close to or cross the orbit
of Earth) spotted by astronomers.

Boynton is a scientist on the X-Ray/Gamma Ray Spectrometer, or XGRS,
experiment. It is the primary experiment for determining the elemental
composition of the surface and layers just beneath the surface. The
instrument will begin taking data next spring while NEAR is orbiting
above the asteroid's surface, coming as close as 9 miles (15
kilometers).

The XGRS was designed and built by the Johns Hopkins University Applied
Physics Laboratory in Laurel, Md., which also built the NEAR spacecraft
and manages the NEAR mission. Boynton and his group at the UA Lunar and
Planetary Laboratory will process XGRS data and manage the data base for
all XGRS data, as well as work on the scientific interpretation of
results. Boynton's UA colleagues on the NEAR mission include Samuel
(Hop) Bailey, project manager, and software specialists Jazbir (Jesse)
Bhangoo and Irina Mikheeva.

XGRS results are basic to solving such mysteries as the source of
meteorites and their relationship to asteroids.

"Eros is a very important asteroid because it is a member of a class
called ‘S' asteroids, which appear to be similar to a rare type of
meteorite on Earth called ‘stony-irons,'which have 50 percent metal and
50 percent silicate. Though the S-asteroids are very common in space,
they do not seem to match many of the meteorites that fall to Earth,"
Boynton said.

"The other half of this problem is that the most common meteorites found
on Earth, called ordinary chondrites, are very common on Earth but
appear to be rare in space. Some people think that ordinary chondrites
might come from S-asteroids and that S-asteroids actually might have a
lower metal content than ground-based astronomical data suggest. This
mission should really answer this question."

It's possible that the composition of Eros might turn out to be
different from any of the known meteorites, Boynton added. It's also
possible that Eros, a highly irregularly shaped object, is "possibly a
chip off some larger, pre-existing asteroid that was smashed up," richer
in silicates on one side and richer in metal on another, Boynton said.
"This might allow us to learn something about the processes that go on
in asteroids."

NEAR is the first in NASA's Discovery Program for "faster, better,
cheaper" planetary missions. It was launched Feb. 17, 1996, from Cape
Canaveral, Fl., 9 months sooner than its 36-month schedule and $41.6
million under the $150 million budget. The other NEAR instruments
include a multispectral imager, a laser rangefinder, a near-infrared
spectrometer, a magnetometer and a radio science package.

NEAR is the first spacecraft powered by solar cells to operate beyond
the orbit of Mars. It returned 500 images of asteroid 253 Mathilde when
it flew within 750 miles of that object on June 27, 1997. Last January
NEAR returned to the Earth's vicinity for a "slingshot" gravity assist
toward Eros' orbital plane.

Next month, Boynton will travel from Cape Canaveral, site of the Jan. 3
launch of the Mars Polar Lander, to the Johns Hopkins lab to witness
NEAR's Jan. 10 arrival at Eros. On the Mars mission, Boynton heads an
experiment in the Mars Volatiles and Climate Surveyor integrated
payload. That experiment, TEGA, or the Thermal and Evolved Gas Analyzer,
is to discover how much water and carbon dioxide is in soil at the south
pole landing site on Mars, and what minerals make up that soil.

EARTH SWINGBY PUTS NEAR SPACECRAFT ON FINAL APPROACH TO EROS

NASA's Near Earth Asteroid Rendezvous (NEAR) spacecraft,
built by The Johns Hopkins University Applied Physics Laboratory
(APL) in Laurel, MD, will become the first interplanetary
spacecraft that can possibly be seen with the naked eye when it
swings by Earth Jan. 22-23. The spacecraft's solar panels will
reflect the Sun's rays onto the Earth in a greeting as it flies by
for an adjustment of its trajectory to correctly align the
spacecraft for a rendezvous with asteroid 433 Eros, its mission target.

Launched Feb. 17, 1996, NEAR completed a flyby of the
asteroid Mathilde in June 1997 and is now on its way back to
Earth. Late Thursday, Jan. 22, the spacecraft will approach Earth
over the Pacific Ocean traveling at about 20,000 mph. Because the
United States will be in darkness as NEAR approaches, if there is
no cloud cover, several geographic areas will be able to see the
Sun reflecting off the spacecraft's solar panels, which will act
as large mirrors. These sunglints will be visible on the East
Coast, Friday, Jan. 23, at about 1:30 a.m. EST and the West Coast
at about 1:45 a.m. EST (Thursday, 10:45 p.m. PST).

The spacecraft then swings around the Aleutian Islands and
over Siberia before reaching its closest point to Earth, about 336
miles above Ahvaz in southwest Iran, Friday, Jan. 23, at 11:23
a.m. local time (2:23 a.m. EST), traveling at about 29,000 mph,
its fastest speed for the swingby. Although NEAR will be close to
Earth at this time, daylight may obscure its image.

The spacecraft then swings over Africa and on to
Antarctica before pulling away from the Earth at a speed of about
15,000 mph. The swingby will have changed NEAR's trajectory to
approximately 11 degrees south of the Earth's ecliptic plane, the
orbital path the Earth takes as it circles the Sun, and put the
spacecraft on target for its Jan. 10, 1999, rendezvous with Eros.

NEAR scientists and engineers are using the swingby as an
opportunity to test performance and calibration of the
spacecraft's six instruments and to practice coordinated multi-
instrument observations of the type that will be used at Eros.

The Multispectral Imager, a visible light camera that will
help determine the physical characteristics of Eros, and the NEAR-
Infrared Spectrograph, used to study surface minerals, will be
calibrated by comparing their readings of geological features with
proven measurements of the same areas. These instruments will
also be used to take images of the Earth along the spacecraft's
path. NEAR's Magnetometer will be calibrated by comparing swingby
data with known measurements of the Earth's magnetic field.

Other activities during the swingby will include using the
X-Ray/Gamma-Ray Spectrometer to observe celestial gamma ray bursts
and to collect data on gamma ray and X-ray backgrounds. These
data are needed so scientists can better remove background
impurities from the measurements to be made at Eros.

NEAR is expected to capture its first images of Eros, a 25-
mile-long near-Earth asteroid, a few months prior to the 100th
anniversary of the asteroid's discovery on
Aug. 13, 1898. After reaching Eros, the spacecraft will start its
orbit about 600 miles above the asteroid's surface, descending to
200 miles by February and coming as close as 10 miles during its
yearlong study. Scientists will thoroughly map Eros and will
examine its surface composition and physical properties. On Feb.
6, 2000, the mission is expected to end with a controlled descent
onto the asteroid, sending dozens of high-resolution pictures as
the spacecraft closes in on Eros.

The NEAR mission will be the first close-up study of an
asteroid. APL, the first non-NASA center to conduct a NASA
planetary mission, is managing the mission for NASA's Office of
Space Science, Washington, DC.

Johns Hopkins University
Applied Physics Laboratory

JHU/APL Office of Public Affairs

NASA Headquarters Office of Space Science

July 3, 1997

Deep Space Maneuver Retarget NEAR for Asteroid 433 Eros Encounter

The trajectory for the Near Earth Asteroid Rendezvous (NEAR) spacecraft was
adjusted at 6:30 a.m. EDT, today, to target the spacecraft for an Earth
swingby in 1998. An 11-minute firing of its bi-propellant engine slowed NEAR
down by 269 meters per second (602 mph) to a current speed of about 18,244
meters per second (41,000 mph) and nudged the spacecraft about half a degree
from its previous path. This maneuver puts NEAR on track for a close Earth
flyby on Jan. 23, 1998, which will bend the spacecraft's trajectory into the
orbital plane of asteroid 433 Eros.

"Everything went beautifully and we are now on target for a rendezvous with
Eros in January 1999," says NEAR Mission Director Dr. Robert W. Farquhar of
The Johns Hopkins University Applied Physics Laboratory (APL), Laurel, Md.,
where NEAR was designed and built. Spacecraft Systems Engineer Andrew G.
Santo, also of the Applied Physics Laboratory, says, "The burn was performed
so accurately that fuel that had been allocated for further correction can
now be used during the orbital phase."

Today's maneuver was the first time the large thruster engine was fired. The
next scheduled firing of the engine, Dec. 20, 1998, will mark the beginning
of the Eros rendezvous sequence.

The flawless deep space maneuver continued the success story of the NEAR
mission that began with its Feb. 17, 1996 launch from Cape Canaveral Air
Station in Florida. On June 27, 1997, the spacecraft completed a flyby of
asteroid 253 Mathilde, sending back spectacular images of a dark, battered
carbon-rich rock believed to date from the beginning of the solar system.
The flyby was the closest look at any asteroid to date and the first
encounter with a C-type (carbon-based) asteroid. The Mathilde images were
the first science return of NASA's Discovery Program. A radio science
experiment measured for the first time the mass of an asteroid.

The NEAR mission, which will end Feb. 6, 2000, after a year-long study of
Eros, will provide the first comprehensive study of a near-Earth asteroid.
The mission has been managed by APL, where the Mission Operation and
the Science Data centers are located.